Magnetic bearings of the above mentioned type are used in many applications, e.g. at disk storages for computers, in domestic machines. Because of the type we used in these applications to achieve silent operation, extended operation life and high rotational accuracy. An important advantage of such bearings is that the lubricant, which contains particles of magnetizable material, is retained in the bearing by the magnetic field generated by the magnetic bearing sleeve, whereby leakage of the lubricant is prevented.
In DE-A-3.304.623 is shown a magnetic bearing incorporating a magnetic bearing sleeve, which on its surface facing the shaft has grooves for causing a hydrodynamic pressure in the magnetic fluid. This device has a complex design and the shape of the grooves furthermore requires that the shaft is rotated in the sam direction all the time.